Fork truck operated switch

ABSTRACT

A safety switch device, particularly for use at a door for a vertically moving conveyor, is provided with a switch plate section immediately adjacent the door for stopping the conveyor upon supporting an operator or the like, is provided with mirror image hinged plate middle sections that will stop the conveyor when engaged by the wheels of a forklift truck, and outer hinged switch plate mirror image sections that will recycle the control circuit so that the conveyor will only start after the sequence of the forklift truck rolling off of the middle switch plate sections and onto the outer recycling switch plate sections to prevent accidental starting of the conveyor if the forklift truck bounces upwardly, pivots upon receiving a load, or otherwise momentarily removes its weight from the middle switch plate section. Each of the switch plate sections is mounted for either pivoting or vertical reciprocating movement from an upward normal position where it is supported on springs to a lower position where it is supported on stationary spacers with the springs compressed, so that such movement will operate suitable micro switches that are mounted for vertical adjustment.

United States Patent Kornylak Nov. 26, 1974 FORK TRUCK OPERATED SWITCH Edward T. Kornylak, Hamilton, Ohio [73] Assignee: jgornylak Corporation, Hamilton,

Ohio

22 Filed: 0ct.23,1973

21 App1.No.:408,423

[75] Inventor:

[30] Foreign Application Priority Data [58] Field of Search 198/40, 154, 158; 340/272, 340/273; 200/18, 52 A, 153 T, 61.58 R,

61.69, 61.7, 61.76, 61.81, 85 R, 86 R, 86 A,

86.5, 5 A, 5 R, 16 A, 16 R [56] References Cited UNITED STATES PATENTS 2,983,358 5/1961 Clemetsen 200/86 R 3,171,914 3/1965 Ohanian Farris Smith 200/865 Primary Examiner-Robert K. Schaefer Assistant ExaminerGerald P. Tolin Attorney, Agent, or FirmThomas E. Beall, Jr.

mrzw

57 ABSTRACT A safety switch device, particularly for use at a door for a vertically moving conveyor, is provided with a switch plate section immediately adjacent the door for stopping the conveyor upon supporting an operator or the like, is provided with mirror image hinged plate middle sections that will stop the conveyor when engaged by the wheels of a forklift truck, and outer hinged switch plate mirror image sections that will recycle the control circuit so that the conveyor will only start after the sequence of the forklift truck rolling off of the middle switch plate sections and onto the outer recycling switch plate sections to prevent accidental starting of the conveyor if the forklift truck bounces upwardly, pivots upon receiving a load, or otherwise momentarily removes its weight from the middle switch plate section. Each of the switch plate sections is mounted for either pivoting or vertical reciprocating movement from an upward normal position where it is supported on springs to a lower position where it is supported on stationary spacers with the springs compressed, so that such movement will operate suitable micro switches that are mounted for vertical adjustmerit.

13 Claims, 3 Drawing Figures FORK TRUCK OPERATED SWITCH BACKGROUND OF THE INVENTION In a vertical conveyor of the type shown in Komylak US. Pat. No. 3,365,052, issued Jan. 23, 1968, trays or shelves are moved between vertical stations or levels, where loading or unloading doors are provided at each station. In view of the hazard of people being injured by reaching into the door at a particular station or the loading forks of a forklift truck extending into the vertical run of the conveyor, while the conveyor is in motion, various safety devices are known which will automatically stop the conveyor upon sensing the approach of a person or forklift truck to the door to gain access to the conveyor at any particular station. However, such devices have not proved to be reliable under the adverse conditions of material handling areas, such as the marine environment of ship level loading and unloading vertical conveyors; that is, they will not take the heavy duty operation over extended periods of time under adverse climate conditions.

SUMMARY OF THE INVENTION The safety device of the present invention is designed to stop the vertical movement of a conveyor, such as the above mentioned Kornylak vertical conveyor, upon sensing the approach of a forklift truck to the door of the conveyor shaft, or the positioning of a human being within close proximity to the conveyor door. The device is of welded steel fabrication with hinged sections that will move downwardly against the predetermined bias of springs for actuating micro switches for the above mentioned sensing, and that will hinge upwardly for access to the interior, for repairs, for adjustment of the switches, for cleaning, and for exchange of the springs to provide a different predetermined bias.

Basically, there are three sensing sections: the first section furthest away from the conveyor door will sense the approach of a forklift truck and condition various relays and the like so that upon further movement of the forklift truck onto the middle section, the switches of the middle section will be able to stop the conveyor, and further the first section will not permit movement of the conveyor thereafter until the first section switch is again actuated as the forklift truck backs out of the conveyor door area; the middle section, upon being depressed, will actuate switches to stop the conveyor after the switches of the first section have previously been actuated, but the middle section will not permit movement of the conveyor even though the middle section is no longer depressed until after the first section switch is again actuated showing that the forklift truck has in fact backed out of the area, which safety feature is designed to prevent movement of the conveyor when the forklift truck may bounce upon entering the switch area or pivot upwardly as it engages a load; the section closest to the conveyor door will stop the conveyor anytime that it is depressed, and its springs may be lighter than the previously mentioned sections so that it wil easily sense the presence of a human being adjacent the conveyor door to stop the conveyor regardless of any previous actuation of the switches forming a part of the other sections.

The two sections that are furthest away from the conveyor door are formed of right and left hand portions, each pivotally hinged to a central stationary member,

so as to form mirror image portions for each section. Each hinged portion will engage rigid stationary portions spaced beneath it so as to support the weight of a loaded forklift truck. Springs are provided to bias each portion upwardly away from the stationary support members, so that the load of a forklift truck will move the section downwardly against the bias to engage the stationary members and at the same time actuate a switch that is mounted for vertical adjustment. The section that is closest to the conveyor is mounted for vertical reciprocation and provided with springs and switches for similar operation.

BRIEF DESCRIPTION OF THE DRAWING Further objects, features and advantages of the present invention will become more clear from the following detailed description of a preferred embodiment of the present invention, as shown in the attached drawing, wherein:

FIG. 1 is a perspective view of the device;

FIG. 2 is a partial cross sectional view taken along line II-II of FIG. 1; and

FIG. 3 is a contra] circuit diagram.

DETAILED DESCRIPTION OF THE DRAWING As shown in FIG. 1, the safety device of the present invention is arranged so that its far end 1 will be immediately adjacent the door opening or vertical wall containing the door opening of a vertical conveyor trunk or shaft, with the device resting upon the floor of the level having the adjacent door. Preferably, one of the safety devices would be placed at each such conveyor opening at the various levels serviced by the conveyor. However, it is understood that the safety device may be used in different similar environments as desired.

The device comprises a stationary ramp 2 extending for almost the entire width of the device, as shown, for providing a smooth transition for the forklift truck or the like as it runs from the floor, up the ramp 2, and onto the device as it moves toward the edge 1 adjacent the door (not shown). The ramp 2 is rigidly connected to a central stationary portion 3, and rigidly connected to a bottom plate 4, which bottom plate is integral with stationary right hand vertical side plate 5 and left hand vertical side plate 6.

A first switch section comprises right hand portion 7 and mirror image left hand portion 8, each of which portions is hinged respectively at 9 and 10 to the stationary central portion 3. A second, middle, switch section is composed of right hand portion 11 hinged to the central stationary section 3 by hinge 13 and left hand portion hinged to the stationary central section '3 by hinge 14.

While FIG. 2 shows a cross section of the mounting for the left hand portion 12 of the central switch section, it is to be understood that the right hand portion is a mirror image thereof, and that a parallel cross section taken centrally through the portion 8 of the first hinged section would be identical to FIG. 2, and correspondingly the right hand portion 7 would bea mirror image. From FIG. 2, it is seen that the central stationary section 3 is composed of a rectangular plate welded to spacer pieces 15 that are in turn welded to the bottom plate 4. The axis of hinge 14 is perpendicular to the plane of FIG. 2, and as shown in FIG. I, the hinge 14 is coaxial with the hinge l0 and parallel with the coaxial hinges 9 and 13. The hinged portion 12 comprises a first sheet metal plate 16 welded along one side to the hinge 14, welded at its opposite side to an angle member 17, and supported along its intermediate portions by resting upon upstanding spacer members 18, 19, that are in turn welded to the bottom plate 4. The

. spacer members may be square cross section rods parallel with each other and extending parallel to the axis 14 for the full length of the plate 16. The angle member 17, as shown, has a lower portion supportingly resting upon the bottom plate 4 to provide further support for the plate 16, and has an opposite end supportingly resting upon the upstanding vertical wall 6 that is integral with the bottom plate 4.

The pivoted switch portion 12 is biased for rotation clockwise about its hinge 14, as viewed in FIG. 2, by means of a spring bias comprising an outer tube 21 welded to the bottom plate 4 and containing therein a coil spring 22, and a piston member 23 received telescopically within the tube 21 for engagement with the spring 22. The horizontal portion of the angle member 17 supportingly rests upon the piston 23, and the spring 22 is designed so that, through the intermediary of the piston 23, it will pivot the switch plate portion 12 upwardly so that the opposite ends of the angle member 17 will be spaced asmall predetermined distance from the wall 6 and bottom plate 4, respectively, and the bottom of the plate 16 will be spaced small distances from the spacer members 18, 19, 20, respectively under no load conditions, that is when there is no forklift truck or the like resting upon the section; however, it is noted that FIG. 2 shows the sectionas it would appear supporting a forklift truck wherein all of the stationary support surfaces are engaged.

A switch member is provided to sense the support of a forklift truck on the switch plate section, and comprises a switch abutment 23 welded to the underside of the horizontal portion of the angle member 17 for engagement with the movable contact 24 of a micro switch (not shown in detail, because it is conventional), which micro switch is carried on a movable support member 25 that is provided with an external thread for threaded engagement with an internal thread (not shown) of a stationary support tube 26 that is welded to the bottom plate 4. It is thus seen that turning of the movable support member 25 will, due to the threaded connection, move the micro switch contact 24 upwardly or downwardly depending upon the direction of rotation for adjustment of the switch so that the switch will be in either its open or closed position in the load position of FIG. 2 and in its opposite position when the load is removed and the plate 16 and angle member 17 are pivoted clockwise about the hinge 14 under the bias of the spring 22.

It is seen that the angle member 17, bottom plate 4, and vertical wall 6 form an enclosure for the switch assembly 23, 24, 25, 26 and the spring assembly 21, 22, 23, to keep these assemblies relatively clean and protect them from damage. Access to the spring assembly for cleaning, repairing, and exchanging springs to prov vide different preloading and access to the switch assembly for cleaning, repairing, and adjusting may be provided by pivoting the plate 16 and angle member 17 clockwise about the hinge 14 to a vertical position for the plate 16 or beyond.

Since as mentioned above, the corresponding cross sections through switch plate portions 7, 8, 11 would be either identical or mirror images of FIG. 2, further details will not be shown thereof, except that the locations of the switch assemblies and spring assemblies are shown in FIG. 1, although it is understood the actual viewing thereof is prevented in FIG. 1 by the positioning of the respective switch plate portions 7, 8, 11, 12. As shown in FIG. 1, spring assemblies substantially identical to the spring assemblies shown in FIG. 2 are provided inphantom lines indicated by reference numeral 27, and switch assemblies substantially identical to the switch assembly 23, 24, 25, 26 of FIG. 2 are posi tioned as shown in phantom lines in FIG. 1 that are referred to by numeral 28.

The third switch plate assembly 29 that is immediately adjacent the conveyor and forms the edge 1 comprises a central plate 30 extending to and welded to opposite angle members 31 and 32 to extend for the full width of the safety switch device. A vertical cross sectional view taken centrally through switch plate section 29 parallel to line IIII for the full width thereof would have a left hand portion identical to the left hand portion of FIG. 2 extending up to but not including the hinge l4 and a right hand portion that would be a mirror image thereof, with the plate 30 being continuous from the left hand angle member 32 to the right hand angle member 31, and further the structure, location and operation of spacer members l8, 19, 20 rigidly mounted on bottom plate 4 for engaging the plate 29 and spring assemblies and switch assemblies for engaging the angle members 31, 32 would be substantially the same as shown in FIG. 2, so that further illustration is unnecessary and would only unduly complicate the disclosure. Four spring assemblies 33 substantially identical to the spring assemblies shown in FIG. 2 are provided for the spring plate section 29 to mount the section 29 for vertical reciprocation as the load is applied and removed and the respective springs compressed and extended, respectively. Preferably, the piston of each spring assembly is welded to the respective angle member 31, 32 to limit any transverse movement of the section 29, which construction is different from the construction of FIG. 2 wherein the piston 23 merely engages the angle member 17. Further, a switch assembly substantially identical to the switch assembly of FIG. 2 is provided at each opposite end of the switch plate section 29 as shown in phantomlines by numeral 34 in FIG. 1.

OPERATION With use of the safety switch device of the present invention in the environment of a vertical conveyor as above mentioned, a forklift truck that will approach the conveyor door for either loading or unloading purposes, will roll up the stationary ramp 2 so that its front wheels will respectively engage the switch plate sections 7, 8 for pivoting them about their hinges 9, 10 against the bias of their spring assemblies to actuate their switches. An electrical control circuit is provided to operate relays or the like so as to condition the control circuit for subsequent stopping of the conveyor, although actuation of the switches associated with switch plates 7 and 8 will not by itself stop the conveyor. Thereafter, the forklift truck further advances toward the conveyor so that its front wheels will respectively be carried by the switch sections ll, 12 to pivot them about their hinges l3, 14 against the bias of their spring assemblies for actuation of their switches; the actuation of any one of the four switches associated with switch plate portions 11, 12 will stop the vertical conveyor so that the forklift truck may move further to a position where its front forks will reach within the door to engage or deposit a load upon the now stationary conveyor shelf. The length of the safety switch device is such that if the front wheels of a standard length forklift truck were engaging the front plate 29, the rear wheels would be engaging the plates 11, 12 and if the rear wheels were engaging the plates 7, 8, the front wheels would be engaging the plates 11, 12; the control circuit is such that the conveyor will remain stopped during this time that the plates ll, 12 are engaged by the forklift truck wheels for actuating any one of the associated switches. While support of the forklift truck front wheels on the front plate section 29 will actuate its switches to maintain the conveyor in the stopped condition, the switch plate 29 adds very little to the operation of the device with respect to a forklift truck, since the plates 12, 11 will be engaged by the rear wheels of the forklift truck. If in picking up a load or in bouncing over the ramp or the like, the forklift truck pivots or jumps, respectively so as to remove its weight from the switch plates 11, 12 sufficiently to return the switches to their normal no load condition, the conveyor still will not operate due to the conditioning of the circuit by the switch plate sections 7, 8, for example as by means of holding relays and the like. The conveyor will only restart after the load has been removed from the switch plate sections 11, 12 and thereafterthe switches associated with the switch plates 7, 8 are actuated, which sequence can only occur when the forklift truck backs up so that its front wheels first leave the plates ll, 12 and thereafter roll over the plates 7, 8; it is seen that this sequence of switch operations would not occur when the rear wheels leave the plates 11, 12 and roll over the plates 7, 8 because at the time the rear wheels would be rolling over the plates 7, 8, the front wheels would still be engaging the plates 11, 12.

The springs associated with the plates 11, 12, 7, 8 may be of sufficient strength so that an operator or the like may walk on these plates without actuating the associated switches, so that the conveyor may remain in motion. However, at least the springs associated with the safety switch plate 29 will be light enough in construction so that the weight of an operator or the like upon any portion of the switch section 29 will actuate the associated switches at 34 to immediately stop the conveyor regardless of any previous actuation of the switches associated with plates 7, 8, 11, 12.

OPERATION OF THE CONTROL CIRCUIT The control circuit, as shown in FIG. 3, includes an input power line and an output power line 41. A master control switch 42 is closed to provide power to the motor 43 that will run the conveyor through a normally disengaged clutch. Simultaneously, the coil 43C is energized to close the normally open contact 43-1 and close the normally open contact 43-2. Throughout the operation of the safety switch described above, the control circuit will maintain the motor 43 in operation and the switches 43-1 and 43-2 closed.

When a forklift truck, moving toward the conveyor opening, engages the switch plates 7, 8, the switches 44 will be closed and thereafter opened as the forklift truck moves past them onto the central switch plates; the opening and closing of switches 44 will have no effect upon the conveyor operation at this time.

As the wheels of the forklift truck engage the central switch plates, one or more of the switches 45 will be closed to thereby energize relay coil 45C. Energization of relay coil 45C will open switch 45-1, 50 that simultaneous operation of switches 44 will have no effect. Further, energization of coil 45C will close contacts 45-2 and open normally closed contacts 45-3. Opening of contacts 45-3 will open the circuit to deenergize the coil 46C and coil 47C.deenergization of coil 46C will deenergize a solenoid holding the brake disengaged, so

that the spring urged brake will engage for stopping the conveyor, and simultaneously deenergization of coil 47C will disengage the normally disengaged clutch providing the power transmission between the motor 43 and conveyor drive. Thus, the conveyor will stop. When coil 47C is deenergized with stopping of the conveyor, this will allow normally closed switch 47-1 to close and thereby energize the relay coil 48C. Energization of coil 48C will close normally open switch 48-1 to energize coil 49C. Energization of coil 49C will close normally open contact 49-1. Further movement of the forklift truck onto the switch plate 29 will close switches 50 for energization of relay coil 51C, which will thereby open up normally closed contacts 51-1, to further assure that the conveyor will remain stopped.

In this position, the forklift truck will load or unload, as the case may be.

When the forklift truck retreats from the conveyor opening, the wheels will move off of switch plate 29, the contacts 50 will open, the coil 51C will be deenergized, and contacts 51-1 will assume their closed position. However, the conveyor will remain stationary due to the contacts 45-3 being open.

As the forklift truck wheels move off of the switch plates 11, 12, switches 45 will open to deenergize coil 45C, close contacts 45-1, open contacts 45-2 and close contacts 45-3. However, the conveyor will remain stationary, because contact 47-2 remains open and contact 52-1 remains open. At this point, the circuit leading to coil 49C through now open switches 45 and open switch 45.2 is broken, but coil 49C is a latch coil that is held energized; therefore, when coil 49C- was energized as mentioned before with closure of switches 45, it immediately opened switch 49-2 to break the above mentioned circuit, so that coil 49C has its energization circuit immediately broken and is independent of switches 45, so that it remains energized due to its latch nature. Coil 49C being latched, will maintain switch 49-3 in its closed position even after the wheels move off of switch plates 11 and 12 to open switches 45.

After the wheels move off of switch plates 11, 12, they immediately contact the switch plates 7, 8 to close one or more of the switches 45. As mentioned above, switch 49.3 is closed due to latch coil 49C; switch 43-2 is closed due to energized coil, 43C in circuit with the running motor 43; switch 51-2 is in its normally closed condition due to the coil 51C being deenergized; switch 45-1 is in its nonnally closed position due to coil 45C being deenergized. Therefore, coil 52C will be energized to close switch 52-2 to bypass the switches 44, and further to close switch 52-1. It is now seen that switch 52-1 is closed, switch 53-1 is closed due to energized coil 43C, switch 45-3 is in its normally closed condition to deenergized coil 45C and switch 51-1 is in its normally closed position due to deenergized coil 51C, so that coil 46C will be energized to release the brake and simultaneously coil 47C will be energized to engage the clutch and start the conveyor. Energizing coil 47C will close normally open switch 47-2 to maintain the energization of coils 46C and 47C independent of switches 44 and coil 52C. Thereafter, the conveyor clutch engaging coil 47C and brake release coil 46C will be energized through the up or down selector circuit 54 and the closed switches 47-2, 45-3 and 51-1. Further, energization of clutch engaging coil 47C will open normally closed switch 47-1 to deenergize coil 48C; deenergizing coil 48C will open switch 48-2 after a predetermined built in delay of, for example, two seconds. Opening of switch 48-2 will release the latch on coil 49C, to deenergize coil 49C to open switch 49-1, close switch 49-2, and open switch 49-3.

Thus, it is seen that merely opening switches 45 by the wheels of the truck disengaging the switch plates 11, 12 will not start the conveyor, until the wheels engage the switch plates 7, 8 to close switches 44 indicating that the truck has in fact left the area and not merely bounced into the air or pivoted during loading.

If switches 44 were closed while the truck wheels still engaged plates 11, 12, switches 45 would be closed to energize coil 45C and open switch 45-1, so that closing of switches 44 would not energize coil 52C so that the conveyor would not start; that is, it is only the sequence of opening the switches 45 followed by the closing of switches 44.

Preferably the springs associated with switch plates 7, 8, 11, 12 are sufficiently strong that the associated switches 44, 45 will not be closed due to the weight of a man. However, the springs associated with switch plate 29 are sufficiently light that a mans weight upon the switch plate 29 will close the switches 50. It is seen that with closure of switches 50, coil 51C is energized to open switch 51-1, which will set the brake and release the clutch regardless of the condition of any other elements within the circuit.

It is seen that after the conveyor is restarted with energizing of coil 47C, switch 47-1 will be opened to deenergize coil 48C and, with a two second delay, close contact 48-2 for unlatching the coil 49C and deenergizing it. This will open switch 49-3. Thus, any reclosing of switches 44 will have no effect with the conveyor in operation. Further, mere momentary closing of the switches 44 will be sufficient for the above mentioned recycling due to the holding coil 52C closing switch 52-2, and the circuit will remain closed for the above mentioned two second delay of switch 48-2.

While a preferred embodiment of the present invention has been set forth in detail for purposes of illustration and for the advantageous specific features thereof, further embodiments, modifications and variations are contemplated within the spirit and scope of the present invention as determined by the following claims.

What is claimed is:

1. A treadle operated safety switch device, particularly for loading openings of a vertical conveyor, comprising: a stationary base adapted to be mounted on a floor adjacent a conveyor loading and unloading area, having one end of the base being adjacent the loading and unloading area, an opposite end and opposed side walls between said opposite ends; first switch plate means adjacent said one end and extending generally from side to side above said base and being mounted for movement toward and away from said base; second switch plate means extending from side to side adjacent said opposite end above said opposite end above said base and mounted for movement toward and away from said base; third switch plate means extending from side to side between said first and second switch plate means above said base, and being mounted for vertical movement toward and away from said base: spring means between each of said switch plate means and said base for normally biasing the respective switch plate means away from said base with a predetermined spacing therebetween under no load conditions with a predetermined force resisting downward movement of the respective switch plate means; and switch means between each of said switch plate means and said base having an open contact position and a closed contact position, being movable between said positions by movement of the respective switch plate means toward and away from said base; said spring means of said third and second switch plate means having a force sufficient to resist changing the position of the associated switch means upon receiving a load substantially that of a normal human being, but being overcome to change the position of the associated switch means upon receiving a load on the associated switch plate means at least as great as that of a conventional forklift truck; said spring means of said first switch plate means having an effective force resisting change in position of the associated switch means that is substantially less than the spring means force of said third and second switch plate means and being readily overcome by a load within the range of an average human being to change the position of the switch means of said first switch plate means; and circuit means for stopping the associated conveyor upon a change in position of the switch means of either said first switch plate means or said third switch plate means by a load being applied thereto.

2. The device of claim 1, wherein said circuit means further includes means for restarting said conveyor after it has been stopped by said first or third switch means only after the switch means associated with said second switch plate means changes position after the switch means associated with said third switch plate means moves from its load position to its no load position and the switch means associated with said first switch plate means is in its no load position, and said circuit means thereby preventing operating of the conveyor with movement of said first and third switch means to their no load position.

3. The device of claim 2, wherein each of said third and second switch plate means includes a central stationary member secured to said base and extending between said sides from said opposite end toward said one end, and mirror image plates each hinged to said central member at one end and having said spring means and switch means extending between said base and their opposite end; and wherein said first switch means is mounted for only vertical reciprocation toward and away from said base and extends continuously from one side to the other side along said one end, and includes at least one spring means and one switch means on one side and at least one spring means and one switch means on the opposite side between said fist switch plate means and said base; and said central sta- Y tionary member, said mirror image plates, and said first switch plate means extending over the entire base.

4. The device of claim 3, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally ebclose the area of said switch means and spring means.

5. The device of claim 4, including a ramp extending along the entire side to side width-of said opposite end between the floor level of said base and the upper surface of said wheel engaging plates, and being stationarily mounted on said base; each of said angle plates including an inner vertically extending portion having a lower edge engaging said base under the design load compression of said spring means, an integral connection with the adjacent horizontally extending wheel engaging plate immediately above said lower edge, and an outwardly extending horizontal portion overlying the associated spring means, switch means and upstanding base side; means providing rigid engagement between each of said horizontally extending wheel engaging plates and said base in the vertical direction under the spring design load between the associated hinge and angle plates.

6. The device of claim 1, wherein each of said third and second switch plate means includes a central stationary member secured to said base and extending between said sides from said opposite end toward said one end, and mirror image plates each hinged to said central member at one end and having said spring means and switch means extending between said base and their opposite end; and wherein said first switch means is mounted for only vertical reciprocation toward and away from said base and extends continuously from one side to the other side along said one end, and includes at least one spring means and one switch means on one side and at least one spring means and one switch means on the opposite side between said first switch plate means and said base; and said central stationary member, said mirror image plates, and said first switch plate means extending over the entire base.

7. The device of claim 6, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally enclose the area of said switch means and spring means.

8. The device of claim 7, including a ramp extending along the entire side to side width of said opposite end between the floor level of said base and the upper surface of said wheel engaging plates, and being stationarily mounted on said base; each of said angle plates including an inner vertically extending portion having a lower edge engaging said base under the design load compression of said spring means, an integral connection with the adjacent horizontally extending wheel engaging plate immediately above said lower edge, and an outwardly extending horizontal portion overlying the associated spring means, switch means and upstanding base side; means providing rigid engagement between each of said horizontally extending wheel engaging plates and said base in the vertical direction under the spring design load between the associated hinge and angle plates.

9. The device of claim 1, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally enclose the area of said switch means and spring means.

10. The device of claim 9, wherein each of said switch means is mounted for vertical adjustment.

1]. A treadle operated switch, comprising: a stationary base; two mirror image switch plate means generally coextensive with and overlying said base, said switch plate means being horizontally adjacent each other and pivotally connected about parallel axes at their inner adjacent ends to said base; each of said switch plate means including a horizontally extending vehicle wheel engaging plate normally generally horizontally coextensive with the wheel engaging plate of the other switch plate means, and an angle plate having a vertical wall portion with a lower edge engaging said base and being rigidly secured to the adjacent edge of said horizontally extending wheel engaging plate opposite from the hinge connection, and a horizontally extending portion spaced horizontally above the wheel engaging plate to provide upstanding sides to guide the wheels along said wheel engaging plates; said base further having an upstanding side wall spaced outwardly from each vertical wall of each of said angle plates and having an upper terminal edge engaging the horizontal portion of the associated plate, so that said base, side wall and angle plate form an enclosure; spring means within each said enclosure for biasing the associated switch plate means about its hinge connection away from said base; and electrical switch means within each of said enclosures having opened and closed positions, with one of said positions corresponding to the position of said angle plate engaging the associated base side wall under a load against said bias means, and the other of said switch positions corresponding to a predetermined spacing between the associated angle plate and base side wall as determined by the bias of said spring means under no load.

12. The device of claim 11, wherein each of said spring means includes telescoping piston and cylinder members vertically arranged between the associated mounting cylinder rigidly secured to the other of said angle plate and base, and a micro switch having external threads engaging the internal threads of said mounting cylinder for vertical adjustment of the micro switch. 

1. A treadle operated safety switch device, particularly for loading openings of a vertical conveyor, comprising: a stationary base adapted to be mounted on a floor adjacent a conveyor loading and unloading area, having one end of the base being adjacent the loading and unloading area, an opposite end and opposed side walls between said opposite ends; first switch plate means adjacent said one end and extending generally from side to side above said base and being mounted for movement toward and away from said base; second switch plate means extending from side to side adjacent said opposite end above said opposite end above said base and mounted for movement toward and away from said base; third switch plate means extending from side to side between said first and second switch plate means above said base, and being mounted for vertical movement toward and away from said base: spring means between each of said switch plate means and said base for normally biasing the respective switch plate means away from said base with a predetermined spacing therebetween under no load conditions with a predetermined force resisting downward movement of the respective switch plate means; and switch means between each of said switch plate means and said base having an open contact position and a closed contact position, being movable between said positions by movement of the respective switch plate means toward and away from said base; said spring means of said third and second switch plate means having a force sufficient to resist changing the position of the associated switch means upon receiving a load substantially that of a normal human being, but being overcome to change the position of the associated switch means upon receiving a load on the associated switch plate means at least as great as that of a conventional forklift truck; said spring means of said first switch plate means having an effective force resisting change in position of the associated switch means that is substantially less than the spring means force of said third and second switch plate means and being readily overcome by a load within the range of an average human being to change the position of the switch means of said first switch plate means; and circuit means for stopping the associated conveyor upon a change in position of the switch means of either said first switch plate means oR said third switch plate means by a load being applied thereto.
 2. The device of claim 1, wherein said circuit means further includes means for restarting said conveyor after it has been stopped by said first or third switch means only after the switch means associated with said second switch plate means changes position after the switch means associated with said third switch plate means moves from its load position to its no load position and the switch means associated with said first switch plate means is in its no load position, and said circuit means thereby preventing operating of the conveyor with movement of said first and third switch means to their no load position.
 3. The device of claim 2, wherein each of said third and second switch plate means includes a central stationary member secured to said base and extending between said sides from said opposite end toward said one end, and mirror image plates each hinged to said central member at one end and having said spring means and switch means extending between said base and their opposite end; and wherein said first switch means is mounted for only vertical reciprocation toward and away from said base and extends continuously from one side to the other side along said one end, and includes at least one spring means and one switch means on one side and at least one spring means and one switch means on the opposite side between said fist switch plate means and said base; and said central stationary member, said mirror image plates, and said first switch plate means extending over the entire base.
 4. The device of claim 3, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally enclose the area of said switch means and spring means.
 5. The device of claim 4, including a ramp extending along the entire side to side width of said opposite end between the floor level of said base and the upper surface of said wheel engaging plates, and being stationarily mounted on said base; each of said angle plates including an inner vertically extending portion having a lower edge engaging said base under the design load compression of said spring means, an integral connection with the adjacent horizontally extending wheel engaging plate immediately above said lower edge, and an outwardly extending horizontal portion overlying the associated spring means, switch means and upstanding base side; means providing rigid engagement between each of said horizontally extending wheel engaging plates and said base in the vertical direction under the spring design load between the associated hinge and angle plates.
 6. The device of claim 1, wherein each of said third and second switch plate means includes a central stationary member secured to said base and extending between said sides from said opposite end toward said one end, and mirror image plates each hinged to said central member at one end and having said spring means and switch means extending between said base and their opposite end; and wherein said first switch means is mounted for only vertical reciprocation toward and away from said base and extends continuously from one side to the other side along said one end, and includes at least one spring means and one switch means on one side and at least one spring means and one switch means on the opposite side between said first switch plate means and said base; and said central statIonary member, said mirror image plates, and said first switch plate means extending over the entire base.
 7. The device of claim 6, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally enclose the area of said switch means and spring means.
 8. The device of claim 7, including a ramp extending along the entire side to side width of said opposite end between the floor level of said base and the upper surface of said wheel engaging plates, and being stationarily mounted on said base; each of said angle plates including an inner vertically extending portion having a lower edge engaging said base under the design load compression of said spring means, an integral connection with the adjacent horizontally extending wheel engaging plate immediately above said lower edge, and an outwardly extending horizontal portion overlying the associated spring means, switch means and upstanding base side; means providing rigid engagement between each of said horizontally extending wheel engaging plates and said base in the vertical direction under the spring design load between the associated hinge and angle plates.
 9. The device of claim 1, wherein each of said switch plate means includes a horizontally extending wheel engaging plate normally horizontally coextensive with the wheel engaging plates of the other switch plate means, and angle plates rigidly mounted to the outer sides of said wheel engaging plates for movement therewith toward and away from said base and to provide upstanding sides to guide the loading truck wheels toward and away from the conveyor on said wheel engaging plates; and wherein said spring means and said switch means extend between said angle plates and said base, and said base further having opposed upstanding sides engaging said angle plates when said switch plate means are under their design load to generally enclose the area of said switch means and spring means.
 10. The device of claim 9, wherein each of said switch means is mounted for vertical adjustment.
 11. A treadle operated switch, comprising: a stationary base; two mirror image switch plate means generally coextensive with and overlying said base, said switch plate means being horizontally adjacent each other and pivotally connected about parallel axes at their inner adjacent ends to said base; each of said switch plate means including a horizontally extending vehicle wheel engaging plate normally generally horizontally coextensive with the wheel engaging plate of the other switch plate means, and an angle plate having a vertical wall portion with a lower edge engaging said base and being rigidly secured to the adjacent edge of said horizontally extending wheel engaging plate opposite from the hinge connection, and a horizontally extending portion spaced horizontally above the wheel engaging plate to provide upstanding sides to guide the wheels along said wheel engaging plates; said base further having an upstanding side wall spaced outwardly from each vertical wall of each of said angle plates and having an upper terminal edge engaging the horizontal portion of the associated plate, so that said base, side wall and angle plate form an enclosure; spring means within each said enclosure for biasing the associated switch plate means about its hinge connection away from said base; and electrical switch means within each of said enclosures having opEned and closed positions, with one of said positions corresponding to the position of said angle plate engaging the associated base side wall under a load against said bias means, and the other of said switch positions corresponding to a predetermined spacing between the associated angle plate and base side wall as determined by the bias of said spring means under no load.
 12. The device of claim 11, wherein each of said spring means includes telescoping piston and cylinder members vertically arranged between the associated angle plate and base, and a coil spring within said cylinder.
 13. The device of claim 12, wherein said switch means includes an abutment formed on one of said angle plate and said base, and an internally threaded mounting cylinder rigidly secured to the other of said angle plate and base, and a micro switch having external threads engaging the internal threads of said mounting cylinder for vertical adjustment of the micro switch. 